It has been known in the casting of models for dental restoration work to employ brass dowels or pins secured to individual tooth members in the casting. After the casting is completed the individual tooth members are separated by cutting slots into the model between them. The tooth members are then individually removed from the model together with their attached dowels and worked on. Thereafter, they are replaced in the model using the dowels and the dowel receiving bores in the model to insure accurate positioning.
In order to remove individual tooth members from the model it is desirable to apply pressure to the free end of the dowels and thus force the tooth members free of the casting. U.S. Pat. No. 2,851,728 issued to Spaltan et. al. employed a wax plug placed within the wax box in contact with each of the dowels. The casting material was then poured around the plugs and after the casting hardened the wax was melted out leaving an elongated opening through which the dowels could be reached.
U.S. Pat. No. 3,286,350 issued to Cooper disclosed a two piece, pipe shaped core which was secured to the end of a dowel for each tooth in the casting and the casting material poured around it. This process eliminated the wax melting step.
In U.S. Pat. No. 3,461,562 issued to Cooper there was disclosed the use of a jig to support the cores and improve dowel alignment during casting of the model.
U.S. Pat. No. 3,871,804 issued to Cooper showed still another jig and means for placing two dowels in each tooth member to improve the accuracy of positioning.
In present day dental restoration work, it is often preferred to cast a model of the dental impression, grind the cast model down until it is substantially thin, and thereafter drill holes in the model to receive the dowel pins. The dowel pins are cemented into holes and additional casting material is poured around the dowel pins to form a base for the model. Employing this technique, it is still desirable to provide elongated openings in the model to reach the ends of the dowels so that individual tooth members can be ejected from the model.
Accordingly, it is an object of the present invention to provide core members which can be incorporated into the casting of a dental model to give access to the ends of the dowels after the casting has hardened, without the need for jigs.
Another object of the present invention is to provide core members which lend themselves to the use of two or more dowels in a single tooth member without the need for accurate spacing of the dowels.
A further object of the present invention is to provide a core structure which may be used for posterior as well as anterior teeth.
Still another object of the present invention is to provide a core structure which is easy to remove from the casting and which will maintain its position during casting operations without the need for special jigs.